Microscopic Magnetic Resonance Imaging (mu MRI) provides in vivo three dimensional images of the mouse brain at high resolution (approximately 20 mu m) with exquisite soft tissue contrast. In this project we will combine Manganese Enhanced MRI (MEMRI) and Diffusion Tensor Imaging (DTI) to obtain precise maps of activated neuronal circuitry and anatomy in mouse models of importance in studies of drug abuse. Mn2+ acts as an effective MRI contrast agent that it is taken up by active neurons, retained, and passed along neuronal circuitry trans-synaptically. Specific circuits can be probed using focal stereotaxic injections of Mn2+ at different locations. Results obtained in our CEBRA Phase I work indicate that Mn2+ can be detected 3-5 synapses away from the point of injection. In this proposal we will: 1. Map normal neuronal pathways associated with the limbic system building on our Phase IR21 successes in combining T2 weighted, MEMRI, and DTI techniques. Correlate our combined methodology with traditional tract tracing methods. Apply quantitative tools for statistical analysis of 3D MR images using deformation fields and statistical parametric (and nonparametric) maps. These studies will provide a standard atlas of anatomy and activity upon which changes due to altered genotype can be mapped. The same maps will be of general use to map changes due to a myriad of other factors (e.g. drug treatment). 2. Compare and contrast the anatomy and activity of neuronal pathways in mouse models involving disruptions in monoamine neurotransmitters. We will map anatomy and activity with structural MRI, MEMRI, and DTI in: C57BL/6J mice to determine normal anatomy and activity; dopamine (DAT), norepinephrine (NET) and serotonin transporter (SERT) knockouts; dopamine D1 a and D2 receptor knockouts; catechol-O-methyltransferase (COMT) knockout. Experiments will involve recording high resolution three dimensional T2 weighted, DTI, and MEMRI in vivo and subsequently in fixed specimens;data transfer to a Network Accessible Storage system for facile access across the net;warping each data set to a common reference;and detailed statistical analyses of morphological and activity differences. .